She will allegedly eat just two apples a day in order to lose 16lb (1.14 st) in less than 20 days to shoot a tragic scene for the part, reports The Mirror.

"Anne is playing a destitute factory worker-come-lady of the night," an insider said.

"Unfortunately, she only has 15 to 20 days to lose as much weight as possible â€“ up to a stone and a half â€“ because she's been filming the scenes showing her fit and healthy, almost slightly chubby.

"It's not ideal but, as with any high-budget movie, there are strict time constraints."

On how she will lose the weight in such a short timeframe, the source added: "Producers have assigned her a personal trainer and she is literally eating nothing more than a couple of apples a day, and some protein â€“ mainly in the form of a shake.

"Anne knows the risk of such an extreme diet and will undergo weekly medicals to make sure everything is still functioning as it should do."